The use of mobile phones and wireless broadband devices has increased rapidly during the last decade, and it is expected to grow even faster during coming years. To meet these demands, operators must increase the capacity in their communication systems.
In LTE (Long Term Evolution) Advanced, wider bandwidth is achieved by aggregating component carriers either contiguously or non-contiguously. The component carriers are backward compatible with the ones defined in LTE Rel-8. For contiguous carrier aggregation, consecutive spectrum is aggregated. On the other hand, discontinuous bands are accumulated for non-contiguous carrier aggregation.
One way increase capacity in LTE-Advanced is to use reconfigurable antennas at the base station. A reconfigurable antenna is an antenna that can change its properties, for example change tilt, beam direction etc. This could be used to focus the power towards hotspot areas or balancing the load between different cells. To steer the beam in different directions, phase shifters are normally used.
The capacity may also be increased by increasing the frequency bandwidth. However, the available frequency spectrum is limited and to be able to get sufficient large bandwidth, an aggregation of fragmented frequency bands are needed. Two or more bandwidths are then used in combination to increase the bandwidth.
Reconfigurable antennas usually depicts of several antenna elements with individual phase shifters used to steer the beam of the antenna. Each frequency results in a beam. However, the different frequency bands will result in a spatial separation between antenna elements in terms of wavelength. This will cause the beam width to be different for different frequencies. When using aggregated spectrum, this means that different frequency bands will have different beam width, and therefore, also different coverage areas.